I realize the question of effectiveness of masks in preventing Covid has already been asked here several times, but no recent one seems to have a conclusive answer. This article from JustFacts (I know they have a center-right bias, but mediabiasfactcheck.com rates them as "mostly factual") states that masks are ineffective, and that all opinions to the contrary are due to "hysteria" or similar. From a quick read of the article, it appears that they may be cherry-picking data, and some of the experts or studies they quote date back to the first few months of the pandemic.
While I can't address all the details in the article it's clearly being very deceptive:
Covid-19 is mainly spread by microscopic aerosols generated by breathing, talking, sneezing, and coughing. The vast bulk of these infectious aerosols easily penetrate common masks because 90% of the aerosols are less than 1/17th the size of pores in the finest surgical masks, and less than 1/80th the size of pores in the finest cloth masks.
But no mention of N95 masks. Cloth and surgical masks are about stopping exhaling infected droplets, they provide little protection against inhaling them. Thus the size in the air is a red herring in the first place.
Aerosols are light enough to stay airborne for minutes or hours, and hence, they also travel freely through gaps around the edges of cloth and surgical masks.
Which is why you need N95s to protect yourself. Notably not mentioned.
Randomized controlled trials—which are the “gold standard” for clinical research—have repeatedly measured the effects of masks on preventing the spread of contagious respiratory diseases. These trials have found inconsistent benefits from N95 masks in healthcare settings and no statistically significant benefits from any type of mask in community settings.
There are basically no RCTs because you can't ethically have a control group. The closest we have is high grade vs doing what you usually do.
The only randomized controlled trial that evaluated cloth masks found that mandating them causes significant disease transmission in high-risk healthcare settings.
Duh! Cloth isn't much protection.
Because humans create carbon dioxide as they breathe, the CO2 concentration of the air they exhale is about 100 times higher than in fresh air. Masks restrict airflow and thus cause the wearers to rebreathe some of the air they exhale.
But note that they don't address how much air is involved. The trapped volume under a mask is very small, especially for anything less than an N95.
The average CO2 concentrations inhaled by people wearing N95 masks range from 2.6 to 7.0 times OSHA’s work shift limit for CO2. These levels cause headaches and chest pains in some people.
No. This is the CO2 in the air trapped under the mask, not the total inhaled air.
Together, they continue to do so by engaging in actions that resemble common disinformation tactics. These include but are not limited to cherry-picking, censorship, muddying the waters, citation bluffs, non-sequiturs, half-truths, and outright falsehoods.
They're describing their own tactics here.
And let's look at the studies they are using to support their position:
In 2017, the journal Clinical Infectious Diseases published “a systematic review and meta-analysis” about the “effectiveness of masks and respirators against respiratory infections in healthcare workers.” It found that RCTs “indicated a protective effect” from masks but that the “evidence is sparse and findings are inconsistent within and across studies.” It also found that “N95 respirators conferred superior protection” to lower-quality masks.
If N95s do better than others then they must have an effect--thus shooting down their position.
In March 2020, the Journal of Evidence-Based Medicine published a systematic review of six RCTs on masks published in the past five years. It found “there were no statistically significant differences in preventing laboratory-confirmed influenza, laboratory-confirmed respiratory viral infections, laboratory-confirmed respiratory infection and influenza-like illness using N95 respirators and surgical masks.” It only compared these masks to one another and not to using no masks.
And this is supposed to be relevant? So different brands function as well as each other.
8 RCTs in household settings that showed “surgical masks were not associated with decreased risk” for respiratory disease regardless of whether masks were worn by sick people, other people in their households, or everyone.
2 RCTs in college dorms that showed “no significant differences between a surgical mask versus no mask and risk for influenza-like illness.”
2 RCTs among pilgrims to Mecca that showed surgical masks “were not associated with decreased risk for infections,” even when healthy and sick people lived in the same tents.
Not addressing N95s.
It's huge, I'm not going to read the whole thing. Fundamentally, they're showing that cloth and surgical masks offer little protection to the wearer--which is not remotely news. We already know the decent protection for the wearer is N95 and equivalent.